Overfilled bridge structures are frequently formed of precast or cast-in-place reinforced concrete and are used in the case of bridges to support a first pathway over a second pathway, which can be a waterway, a traffic route, or in the case of other structures, a buried storage space or the like (e.g., for stormwater detention). The term “overfilled bridge” will be understood from the teaching of the present disclosure, and in general as used herein, an overfilled bridge is a bridge formed of bridge elements or units that rest on a foundation with soil or the like resting thereon and thereabout to support and stabilize the structure and in the case of a bridge to provide the surface of (or support surface for) the first pathway.
In any system used for bridges, particularly stream crossings, engineers are in pursuit of a superior blend of hydraulic opening and material efficiency. In the past, precast concrete bridge units of various configurations have been used, including four side units, three-sided units and true arches (e.g., continuously curving units). Historical systems of rectangular or box-type four-sided and three-sided units have proven inefficient in their structural shape requiring large side wall and top-slab thicknesses to achieve desired spans. Historical arch shapes have proven to be very efficient in carrying structural loads but are limited by their reduced hydraulic opening area. An improvement, as shown and described in U.S. Pat. No. 4,993,872, was introduced that combined vertical side walls and an arched top that provided a benefit with regard to this balance of hydraulic open area to structural efficiency. One of the largest drivers to structural efficiency of any culvert/bridge shape is the angle of the corners. The closer to 90 degrees at the corner, the higher the bending moment and therefore the thicker the cross-section of the haunch needs to be. Thus, the current vertical side and arch top shape is still limited by the corner angle, which while improved is still at one-hundred fifteen degrees.
A variation of the historic flat-top shape has also been introduced, as shown in U.S. Pat. No. 7,770,250, that combines a flat, horizontal top with an outwardly flared leg of uniform thickness. The resulting shape provides some improvements to hydraulic efficiency versus the flat-top by adding open area and also provides some improvement structurally by flattening the angle between the top and legs to about one-hundred ten degrees. However, flat-tops are severely limited in the ability to reach longer spans needed for many applications (e.g., the effective limit for flat top spans is in the range of thirty to forty feet).
An improved bridge system would therefore be advantageous to the industry.